The high prevalence of myopia worldwide and its prominence as a public health issue emphasize the importance of investigating promising treatments for myopic children, as was done in the Correction of Myopia Evaluation Trial (COMET), and of gaining increased understanding of mechanisms of eye growth, as proposed in the following aims which will analyze 13 years of follow- up data from the COMET cohort. COMET enrolled 469 ethnically diverse myopic children, who provided standardized, reliable measurements of refractive error and ocular components from both eyes. Retention was 99% after 3 years of follow-up and 79% after 13 years. This valuable dataset presents a unique opportunity to investigate mechanisms of eye growth eventuating in astigmatism and anisometropia as well as myopia, topics not addressed in the original aims. Given the reported association between astigmatism and myopia, a key unanswered question is how optical asymmetries in the anterior segment underlying astigmatism are related to axial elongation underlying progressing myopia. Most COMET analyses were child-based, using the average of the two eyes rather than each eye separately, as planned for some of the new analyses. Little is known about the mechanism of different growth rates in the two eyes resulting in anisometropia, which also will be investigated. For most participants the early years of COMET were associated with rapid eye growth and myopia progression, with slower eye growth and myopia stabilization in the later years, thus allowing for an investigation of mechanisms at different stages. The results of these analyses will elucidate factors related to growth in the front and back of the eye, and between the two eyes, and help to determine if eye growth resulting in astigmatism and anisometropia is mainly passive (pre-programmed) or active (visually-guided). The new data also may be used to update clinical guidelines for correction of myopia, astigmatism, and anisometropia.